Facing up to the fungus

WWCT Paignton Zoo - 13th Sep, 2017

Emerging infectious diseases are now recognized as one of the primary threats to human and ecosystem health. Several of the diseases most damaging to animal and plant populations have been shown to be caused by fungal or fungal-like organisms. The most prominent of recently identified fungal pathogens is the chytridiomycete species Batrachochytrium dendrobatidis (Bd) and the closely related B. salamandrivorans (Bsal). These fungi cause chytridiomycosis in amphibians and are responsible for the greatest disease-driven loss of biodiversity ever documented. Bd is known to infect over 500 species of amphibian across more than 50 countries, including the UK, and has been recorded on every continent where amphibians occur. It is responsible for the local extinction of up to 40% of amphibian species at study sites and has been implicated in the global extinction of over thirty species in Central America.

The current detection protocol is based on amplification of DNA and therefore necessitates access to a molecular lab and potentially lengthy delays between swabbing a specimen (in captivity or the wild) and obtaining a result. Following on from experiences conducting chytrid surveys in Tanzania and quarantining captive amphibians at WWCT’s zoos we realized the enormous potential of a rapid diagnostic test that could be used without access to specialist equipment. Colleagues at the University of Exeter have developed antigen-based lateral flow devices for rapid detection of fungal pathogens, similar to a commercial pregnancy test, and so we collaborated to do the same for chytrid fungus through a research grant from the Leverhulme Trust.

So far, the project has successfully generated a monoclonal antibody specific to Bd and Bsal. The antibody, which binds to a glycoprotein antigen present on the surface of all life stages of the fungus, was used to develop a lateral-flow device for rapid (15 minute) detection of the pathogens in the field. The test detects all known lineages of Bd and Bsal but does not detect a wide range of related and unrelated fungi and oomycetes likely to be present in amphibian habitats. When combined with a simple swabbing procedure, the test was 100% accurate in detecting the antigen in tissue samples from frogs and salamanders naturally infected with Bd or Bsal but requires testing on a larger variety of species and infection loads. To this end, we are working with conservation partners in nine countries to test the prototype device on many different species.

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